| 摘要 |
PURPOSE:To make the junction capacitances at the time of reverse bias and the resistances at the time of forward bias of two facing diodes for preventing electrostatic breakdown identical and give the two diodes the same the absorptance for positive and negative surges by giving the two diodes for preventing electrostatic breakdown the same shape. CONSTITUTION:A polycrystalline silicon layer is formed on a silicon oxide film 8 covering a silicon semiconductor substrate 7 in which elements 6 such as resistors are formed as a rectangular island region 13. At the center part of the rectangular island region 13, a P-type diffused region 14 is provided and N-type diffused regions 15 and 16 of the same shape are provided on both sides of the region 14. In other words, a 1st diode for preventing electrostatic breakdown is composed of the n-type diffused region 15 and the P-type diffused region 14 and a 2nd diode for preventing electrostatic breakdown is composed of the P-type diffused region 14 and the N-type diffused region 16 and, as a whole, the 1st and 2nd diodes for preventing electrostatic breakdown are connected in series with opposite polarities. Moreover, as the diodes are provided symmetrically, the junction capacitances at the time of reverse bias and the resistances at the time of forward bias are identical and the respective diodes have the same surge absorptance.
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